Datasheet

EXCHANGE SERVER ARCHITECTURE 17
Figure 1.7
Traditional MAPI to
Exchange connectivity
Outlook MAPI/RPC client
Domain controller/
global catalog server
System Attendant
Information Store
Exchange 2003
Server
Second, the client connects to the RPC interface provided by the Information Store service
(store.exe). This means that the Outlook RPC client is connected directly to the information
store on the Exchange server on which their mailbox database resides.
Although this works just fine for earlier versions of Exchange Server, this makes building a
version of Exchange t hat allows failover at the database level rather than the server level much
more difficult. The Exchange developers had to find a new way to allow Outlook clients to con-
nect both to their mailbox database and to the directory. Rewriting how Outlook works was not
an option since Exchange 2010 has to be backward compatible with earlier versions of Outlook
such as Outlook 2003 and 2007.
The solution is to ‘‘abstract’’ the MAPI interface out of the Mailbox server’s System
Attendant and Information Store services. Rather than having the Outlook MAPI client connect
directly to the Mailbox server, the Outlook client connects to a service that proxies the connec-
tions to the server on which the active mailbox database currently resides. The mailbox store
access and directory access functions are being moved out to the ‘‘middle tier.’’ The middle tier
is a software/service layer that is designed to sit between the client and the actual data source.
Abstracting the directory referrals or directory access out of the System Attendant is called
the Address Book Service (or sometimes called directory on the middle tier) while abstract-
ing the MAPI access layer out is called the RPC Client Access Service (or sometimes called
MAPI on the middle tier). These abstracted functions are now part of the Exchange Server 2010
Client Access server role. Figure 1.8 shows an example of how this might work. A user whose
mailbox database is on the Marketing database opens Outlook. For directory and mailbox
database access, Outlook connects to a Client Access server. The Client Access server acts as
the endpoint for Outlook global address lookups. This is a change from previous versions
of Exchange where the server might provide the Outlook client with a referral to the nearest
global catalog server. In Figure 1.8, the Client Access servers are load balanced for redundancy.
The Microsoft Exchange RPC Client Access service then looks up the Exchange server on
which the user’s mailbox database (the Marketing database in this case) is active and proxies
MAPI requests for mail data to that server. If the mailbox database is in a DAG and fails over
to another server, the connection will automatically be established with the new active server.
One Outlook client connectivity component that remains the same in Exchange Server 2010
is public folder server connectivity. Outlook continues to connect directly to the Exchange